Add exercise rotational-cipher (#975)

config.json

@@ -1091,6 +1091,20 @@
           "control_flow_loops",
           "structs"
         ]
+      },
+      {
+        "slug": "rotational-cipher",
+        "name": "Rotational Cipher",
+        "uuid": "3adbc85c-7e7e-4122-a37d-c843196bc8af",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2,
+        "topics": [
+          "control_flow_if_statements",
+          "control_flow_loops",
+          "memory_management",
+          "strings"
+        ]
       }
     ]
   },

exercises/practice/rotational-cipher/.docs/instructions.md

@@ -0,0 +1,29 @@
+# Instructions
+
+Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.
+
+The Caesar cipher is a simple shift cipher that relies on transposing all the letters in the alphabet using an integer key between `0` and `26`.
+Using a key of `0` or `26` will always yield the same output due to modular arithmetic.
+The letter is shifted for as many values as the value of the key.
+
+The general notation for rotational ciphers is `ROT + <key>`.
+The most commonly used rotational cipher is `ROT13`.
+
+A `ROT13` on the Latin alphabet would be as follows:
+
+```text
+Plain:  abcdefghijklmnopqrstuvwxyz
+Cipher: nopqrstuvwxyzabcdefghijklm
+```
+
+It is stronger than the Atbash cipher because it has 27 possible keys, and 25 usable keys.
+
+Ciphertext is written out in the same formatting as the input including spaces and punctuation.
+
+## Examples
+
+- ROT5 `omg` gives `trl`
+- ROT0 `c` gives `c`
+- ROT26 `Cool` gives `Cool`
+- ROT13 `The quick brown fox jumps over the lazy dog.` gives `Gur dhvpx oebja sbk whzcf bire gur ynml qbt.`
+- ROT13 `Gur dhvpx oebja sbk whzcf bire gur ynml qbt.` gives `The quick brown fox jumps over the lazy dog.`

exercises/practice/rotational-cipher/.meta/config.json

@@ -0,0 +1,21 @@
+{
+  "authors": [
+    "ahans"
+  ],
+  "files": {
+    "solution": [
+      "rotational_cipher.c",
+      "rotational_cipher.h"
+    ],
+    "test": [
+      "test_rotational_cipher.c"
+    ],
+    "example": [
+      ".meta/example.c",
+      ".meta/example.h"
+    ]
+  },
+  "blurb": "Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Caesar_cipher"
+}

exercises/practice/rotational-cipher/.meta/example.c

@@ -0,0 +1,21 @@
+#include "rotational_cipher.h"
+
+#include <ctype.h>
+#include <stdlib.h>
+#include <string.h>
+
+char *rotate(const char *text, int shift_key)
+{
+   char *rotated = malloc(strlen(text) + 1);
+   char *out = rotated;
+   for (const char *in = text; *in != '\0'; ++in, ++out) {
+      if (isalpha(*in)) {
+         const char base = isupper(*in) ? 'A' : 'a';
+         *out = base + ((*in - base + shift_key) % 26);
+      } else {
+         *out = *in;
+      }
+   }
+   *out = '\0';
+   return rotated;
+}

exercises/practice/rotational-cipher/.meta/example.h

@@ -0,0 +1,6 @@
+#ifndef ROTATIONAL_CIPHER_H
+#define ROTATIONAL_CIPHER_H
+
+char *rotate(const char *text, int shift_key);
+
+#endif

exercises/practice/rotational-cipher/.meta/tests.toml

@@ -0,0 +1,40 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[74e58a38-e484-43f1-9466-877a7515e10f]
+description = "rotate a by 0, same output as input"
+
+[7ee352c6-e6b0-4930-b903-d09943ecb8f5]
+description = "rotate a by 1"
+
+[edf0a733-4231-4594-a5ee-46a4009ad764]
+description = "rotate a by 26, same output as input"
+
+[e3e82cb9-2a5b-403f-9931-e43213879300]
+description = "rotate m by 13"
+
+[19f9eb78-e2ad-4da4-8fe3-9291d47c1709]
+description = "rotate n by 13 with wrap around alphabet"
+
+[a116aef4-225b-4da9-884f-e8023ca6408a]
+description = "rotate capital letters"
+
+[71b541bb-819c-4dc6-a9c3-132ef9bb737b]
+description = "rotate spaces"
+
+[ef32601d-e9ef-4b29-b2b5-8971392282e6]
+description = "rotate numbers"
+
+[32dd74f6-db2b-41a6-b02c-82eb4f93e549]
+description = "rotate punctuation"
+
+[9fb93fe6-42b0-46e6-9ec1-0bf0a062d8c9]
+description = "rotate all letters"

exercises/practice/rotational-cipher/makefile

@@ -0,0 +1,37 @@
+### If you wish to use extra libraries (math.h for instance),
+### add their flags here (-lm in our case) in the "LIBS" variable.
+
+LIBS = -lm
+
+###
+CFLAGS  = -std=c99
+CFLAGS += -g
+CFLAGS += -Wall
+CFLAGS += -Wextra
+CFLAGS += -pedantic
+CFLAGS += -Werror
+CFLAGS += -Wmissing-declarations
+CFLAGS += -DUNITY_SUPPORT_64 -DUNITY_OUTPUT_COLOR
+
+ASANFLAGS  = -fsanitize=address
+ASANFLAGS += -fno-common
+ASANFLAGS += -fno-omit-frame-pointer
+
+.PHONY: test
+test: tests.out
+	@./tests.out
+
+.PHONY: memcheck
+memcheck: ./*.c ./*.h
+	@echo Compiling $@
+	@$(CC) $(ASANFLAGS) $(CFLAGS) test-framework/unity.c ./*.c -o memcheck.out $(LIBS)
+	@./memcheck.out
+	@echo "Memory check passed"
+
+.PHONY: clean
+clean:
+	rm -rf *.o *.out *.out.dSYM
+
+tests.out: ./*.c ./*.h
+	@echo Compiling $@
+	@$(CC) $(CFLAGS) test-framework/unity.c ./*.c -o tests.out $(LIBS)

exercises/practice/rotational-cipher/rotational_cipher.c

@@ -0,0 +1 @@
+#include "rotational_cipher.h"

exercises/practice/rotational-cipher/rotational_cipher.h

@@ -0,0 +1,6 @@
+#ifndef ROTATIONAL_CIPHER_H
+#define ROTATIONAL_CIPHER_H
+
+char *rotate(const char *text, int shift_key);
+
+#endif